Solder flux is used for the purposes of activation of the solder and of improving its wetting properties. Since the fluxes have appropriate fluidity, they tend to penetrate, due to the capillary effect, inside the housing through-holes and into the spaces between the pressure sections of the contacts. The flux which penetrated into the contacting sections of the contacts may lead to deterioration of the contacting characteristics. Therefore, a number of techniques have been proposed for preventing the flux from penetration. These techniques can be divided into two large categories: one consisting of an increase in the gap between the press-in section of the contacts and the walls of the through-holes thereby reducing the capillary effect; and the other consisting of a tight sealing around the circumference of the press-in section of the contact.
FIG. 7 represents a plan cross-section of an example of the first technique (JP Patent No. (1991)-238719). The internal wall of the contact-mounting openings 102 of the housing 100 has curved pressure surface 104 of the same curvature as the internal curve 112 of the contact 110 made of a thin sheet. Boss 106 is provided to press the outer surface 114 of the contact 110 with the distance between the boss 106 and the pressure surface 104 being slightly smaller than the thickness of the sheet from which the contact 110 is made. The contact 110 does not form any capillary conduits with the walls of the contact-mounting opening 102, except for the area of the pressure surface 104 and the boss 106, thereby eliminating penetration of the flux.
FIG. 8 is a plan cross section illustrating the second type of measures against capillary effect. The pressure section 202 of the contact 200 stamped out of a metal sheet is of a rectangular shape, and it is pressed into the opening 212, which is slightly smaller than the pressure section of the housing 210. Since the pressure section 202 forms a tight seal along the entire perimeter of the opening 212, flux cannot penetrate between the internal walls of the opening and the pressure section 202.
However, in the first case, the gaps in the areas 120 adjacent to the boss 106 are very narrow, and the flux can penetrate through them by capillary effect. Other areas of possible flux penetration are shown in FIG. 7 by a dotted line; they appear if the contact 110 is placed off-center inside the contact-mounting opening 102, thereby making it possible for the flux to flow through the section 122 where the contact is closest to the side wall of the opening.
In the second type of configuration, the stamped contact may have various types of defects at the surface 204, such as rounded-off corners 206 as shown in FIG. 9. Additionally, unevenness 209 of the punched-out surface 208 can lead to the formation of capillary channels between the walls of the opening 212 and the contact surface thereby making it possible for the flux to penetrate to the tips of the contacts. It is possible to eliminate these channels by increasing-the interference between the contact and the opening. However, this can result in a considerably increased reaction in the housing concentrating in the corners of the opening 212 and leading to a formation of cracks 214. It is also possible to improve the quality of the contacts by stamping them from strips of a square cross section, but this method is applicable to only male post-type contacts.
Therefore, the purpose of this invention is to solve the above mentioned problems and to offer a connector free of the flux penetration due to the capillary effect in which no formation of cracks takes place in the housing and there is no limit on the type of contacts used in the connector.